The present invention relates to an image processing apparatus and an image processing method which perform color processing for input image data.
Generally, conventional image processing apparatuses represented by printers which form images on the basis of input color image data receive RGB signals as color signals for a monitor, performs color processing for the RGB signals, and converts the signals into CMYK signals as output color signals for a printer.
An example of the color processing performed by a conventional, general image processing apparatus is described below with reference to FIG. 18. FIG. 18 is a block diagram showing the detailed arrangement of a color processor for performing color processing in the image processing apparatus. In FIG. 18, multivalue data as input values which are expressed by an RGB color system are applied to a color converting unit 80. The color converting unit 80 converts the data into CMYK multivalue signals by color conversion processing. This color conversion processing performed by the color converting unit 80 is described later. The output CMYK multivalue signals from the color converting unit 80 are applied to a binarizing unit 81, where the signals are converted to CMYK binary signals in the form by which an output unit outputs the data.
As discussed above, the color processing in a conventional image processing apparatus is to convert input multivalue signals expressed by the RGB color system into CMYK binary signals which an output unit uses to output the data.
In a conventional image processing apparatus of the above type, one problem which arises when color reproduction is actually performed is the difference between the range of the color reproducibility of the input side and that of tie output side. For example, a monitor is a light-emitting device which reproduces colors by performing an additive process for light-source R, G, and B signals, whereas a printer is a device which reproduces colors by performing a subtractive process for C, M, Y, and K inks.
The subtractive process is described with reference to FIG. 19. In FIG. 19, reference numeral 150 denotes the surface of a recording medium; 151, 152, 153, and 154, inks of K (black), C (cyan), M (magenta), and Y (yellow), respectively; and 155 and 156, incident light and reflected light to and from the paper surface 150. As illustrated in FIG. 19, in an image processing apparatus such as a printer the K, C, M, and Y inks 151 to 154 are usually output to overlap each other on the paper surface 150. In this instance the incident light 155 reaches the paper surface 150 through the ink layers 151 to 154. The incident light 155 is then reflected by the paper surface 150, is again transmitted through the ink layers 151 to 154, and reaches an observer as the reflected light 156. During the course of the transmission and reflection, energy absorptions sequentially occur in the ink layers 151 to 154 at different spectral absorbance. Consequently, the spectral composition of the light changes, and this reproduces a color.
Due to the difference between the color reproduction methods as described above, the color reproduction range of a monitor is different from that of a printer; normally, the color reproduction range of a monitor is wider.
Generally, printers which perform a color output action receive RGB signals, form CMYK signals by color processing such as color space compression, and reproduce a color by performing the subtractive process for the inks of the CMYK signals.
Some printers which perform processing such as the color space compression discussed above, particularly some ink-jet printers have a function of changing the output scheme in order to meet the demands of a user, e.g., increasing the output speed or improving the output quality.
When the output scheme is changed in this way, the color reproduction range of an output image also changes accordingly. Therefore, it is desirable to selectively use color processing including color space compression in accordance with the change in the output scheme. Unfortunately, in conventional image processing apparatuses only one color space compression method is provided in an output unit. Consequently, it is not possible to selectively use color space compression methods according to the output scheme. This makes it impossible to perform an optimum color reproduction corresponding to the output scheme.
Likewise, the color reproduction range also changes in accordance with the type of recording medium on which an image is to be formed. However, no conventional methods can perform an optimum color reproduction corresponding to the recording medium.